Aquaporins (AQPs) are membrane water channels expressed in many mammalian tissues that carry out fluid transport. This competitive renewal builds on our discoveries of three novel, unanticipated AQP functions - cell migration, cell proliferation and neuroexcitation - each with the potential to yield new therapies for human diseases. The proposed studies utilize cell and mouse models of AQP gene deletion, knockdown and overexpression, and state-of-the-art biophysical methods. Aim 1 will elucidate cellular mechanisms of AQP-facilitated cell migration. Biophysical studies will be done to test the hypothesis that AQP expression in membrane protrusions in migrating cells facilitates water influx and lamellipodial dynamics. Aim 2 will elucidate cellular mechanisms of AQP3-facilitated cell proliferation. The hypothesis will be tested that AQP3-faciliated glycerol transport alters cellular glycerol metabolism, which is a key determinant of cellular ATP/energetics, MAPK signaling and biosynthesis. Aim 3 will elucidate the cellular mechanisms by which AQP4 facilitates the neurotransmission function of electrically excitable cells. Biophysical methods, including novel K+-sensitive fluorescent indicators developed by our lab, will be used to test our working hypothesis that AQP4 expression facilitates K+ reuptake by glial cells following neuroexcitation by an indirect osmotic mechanism involving solute-solvent coupling. In addition to establishing new paradigms on the physiological functions of AQPs, the proposed research will provide a rational basis for identification of AQP modulators for tumor therapy, accelerating wound repair, and medical management of epilepsy.